POOL New / ReutersQueen Elizabeth in Buckingham Palace, after recording her Christmas Day television broadcast to the Commonwealth, Dec. 10, 2014.

At the lunch, Markle will be introduced to all of Prince Harry's extended family — around 50 guests in total — and she'll have to adapt quickly to all the Christmas traditions the Royal Family holds dear — from those steeped in history to the quirky new ones.

1. Christmas Eve is the start of the celebrations at Sandringham. The Queen and Prince Philip depart London after the pre-Christmas lunch and stay in Sandringham until mid-February. Christmas Eve dinner starts promptly at 8 p.m. in full black-tie, but despite the formality, it is the perfect time for the family to relax and catch up.

3. Christmas morning starts with a full English breakfast before the family heads to St. Mary Magdalene Church for the Christmas Day service. The Queen always attends, but made headlines last year when she missed the church service due to a heavy cold. Her absence caused panic across the globe as many feared the severity of the cold could be the undoing of the then 90-year-old monarch.

4. The Queen's annual Christmas Day Speech airs at 3 p.m. to which the Royal Family gathers together to watch. Filmed beforehand, the material of the speech is kept top secret with Queen Elizabeth even writing it herself.

However, it would be safe to assume she will congratulate her grandson, Prince Harry, and his future bride, Meghan Markle, as well as mention London hosting the Commonwealth Heads of Government Meeting in April 2018.

5. Former royal chef Darren McGrady told Good Housekeeping about his favourite tradition: being served by the Queen!

McGrady recalled: "Right before the Christmas buffet, the senior chef on duty goes into the dining room and carves the rib roast or turkey or ham and once he's done, Her Majesty presents the chef with a glass of whiskey and they toast. That's the only time the chef goes into the dining room and has a glass of whiskey with the Royal Family. It's one of the chef's favourite traditions."

HuffPost

6. Christmas presents are opened on Christmas Eve. McGrady further explained that since the Royal Family is of German descent (on Prince Philip's side and the Queen's patrilineal side) they keep some of those traditions and exchange gifts after afternoon tea on Christmas Eve. The gifts are displayed on a table and the family takes turns opening them in front of each other.

7. No extravagant gifts either. Instead of luxurious presents, they find gag gifts for each other. It has been reported that Princess Anne has given Prince Charles a white leather toilet seat and the Duchess of Cambridge gave a then-single Prince Harry a "grow your own girlfriend" kit.

8. Their extravagance also doesn't extend to the décor. While Buckingham Palace is dressed to the nines, Sandringham is their private residence, and the Queen prefers minimal decorations, including a fake Christmas tree that has been around for 30 years.

9. All the celebrations would tire out even the most experienced partier, but you won't find yourself crawling into bed before the Queen. No one is allowed to retire before Her Majesty and it is said she loves a good game of charades and won't be found in bed before midnight.

10. Christmas wouldn't be complete without Christmas cards and the Royal Family sure knows how to do them! Dating back to 1914 when King George V and Queen Mary first sent a card to the troops, the typically secluded family uses this time of year to release unseen pictures; the ultimate gift for any royal fan!